This application claims benefit of Japanese Application No. Hei 11-161393 filed in Japan on Jun. 8, 1999, and Japanese Application No. Hei 11-196511 filed in Japan on Jul. 9, 1999, the contents of which are hereby incorporated by reference.
1. Field of the Invention
This invention relates to an ultrasonic vibrator for generating ultrasonic vibrations by supplying a high frequency current to a vibrating element.
2. Description of Related Art
Recently, the use of an ultrasonic surgical apparatus, which comprises an ultrasonic vibrator, by which various surgical operations are performed, such as destruction of a calculus or removal of a tumor, has come into practical use. The ultrasonic surgical apparatus comprises a handpiece in which the ultrasonic vibrator is incorporated, and a driving power supply unit that is connected to the handpiece and supplies a driving current to the ultrasonic vibrator.
The ultrasonic surgical apparatus for surgical operations can be used in an abdominal operation or a laparoscopic operation generally by attaching various probes to a device (i.e., vibrator) that receives a high frequency current from a power-supply unit, and generates ultrasonic vibrations.
This type of surgical apparatus must be sterilized because it is handled by a surgeon directly with his/her hand. The vibrator of the ultrasonic surgical apparatus must also be subjected to autoclave sterilization.
Such a vibrator is disclosed in, for example, U.S. Pat. No. 5,395,240, Japanese Patent Publication No. Hei 7-106206, and Japanese Laid-open Patent Publication No. Hei 10-127655.
There are many kinds of autoclave sterilization methods, each determined by a combination of parameters of time, pressure, temperature, etc., in a vacuum drawing step, a sterilizing step, a drying step, and so on.
The ultrasonic vibrator is not adaptable to all these autoclave sterilization methods. Normally, autoclaving includes the cycle of vacuum drawing, sterilizing, and drying steps. At times the autoclaving is urgently performed when the surgical apparatus is carelessly dropped onto a floor during surgery.
In such event, the vacuum drawing and sterilizing steps is performed and the drying step is omitted to save time. By omitting the drying step often causes steam that has entered the casing is not completely expelled therefrom, and, accordingly, the steam collects in the form of drops of water in the casing, for example, in the casing of a vibrator disclosed in Japanese Patent Publication No. Hei-106206. If ultrasonic vibrations are started under this state, in a bolt-fastened Langevin vibrator (transducer), the drops of water adhere between electrodes between which a PZT (lead zirconate titanate) is disposed, and a short circuit is caused, thus decreasing the conversion efficiency of the ultrasonic wave.
When autoclave sterilization is simply performed in a small medical institution, the autoclave sterilization often does not include the drying step. Also, in this situation, as in the previous situation, drops of water collect in the casing, and, as a result, in a bolt-fastened Langevin vibrator (transducer), the water adheres between electrodes between which a PZT (lead zirconate titanate) is disposed, and a short circuit is caused, thus decreasing the conversion efficiency of the ultrasonic wave.
The invention of U.S. Pat. No. 5,395,241 is a magnetostrictive vibrator (transducer), and therefore no problem occurs even if the inside thereof is intentionally subjected to autoclave sterilization. However, the magnetostrictive vibrator is inferior in washability. From the viewpoint of the reduction in the size of a vibrator, a bolt-fastened Langevin type vibrator (transducer) is greatly superior thereto.
In the invention of Japanese Laid-open Patent Publication No. Hei 10-127655, steam does not enter the inside of a vibrator when autoclave sterilization without a drying step is performed, and therefore the conversion-efficiency of ultrasonic vibrations does not decrease. However, there is a drawback in that smooth rotation cannot be made because an O-ring is used for a rotation slide portion, and there is a concern that electric contact will become unreliable because an electric contact portion is rotating. Additionally, there is a drawback in that the weight of the vibrator increases, and the outer diameter thereof is enlarged because the internal structure of the vibrator becomes complex. From the viewpoint of the versatility of the vibrator, the structure of the vibrator should be simple, of course.
In this type of ultrasonic surgical apparatus, the ultrasonic vibrator is driven at a resonance point in order to efficiently perform the surgery. Specifically, when the ultrasonic vibrator is driven, an oscillation frequency is controlled so that a phase difference between a voltage applied to the ultrasonic vibrator and a flowing current reaches zero by the use of PLL (phase-locked loop), and thereby the resonance point is pursued.
By the way, an equivalent circuit of the ultrasonic vibrator generally has a structure in which a braking condenser (braking capacitive component) is connected in parallel with a series resonance circuit in which a coil L, a condenser C, and a resistor R are connected in series. When a voltage is applied to such an ultrasonic vibrator, a current flows through both the braking condenser and the series resonance circuit. However, only the current flowing through the series resonance circuit of the two is converted into ultrasonic vibrations. Therefore, it is most efficient to drive the vibrator at the resonance point (mechanical resonance point) of the series resonance circuit.
Concerning a technique to drive the series resonance circuit at its resonance point (mechanical resonance point), many proposals have been offered heretofore. For example, in Japanese Patent No. 2,898,010, a composite capacitance value in a handpiece is kept constant, and a capacitive component (condenser) by which the composite capacitance value is equalized with an inductance of an inductive component (inductor) L of a driving power-supply unit, is connected in parallel with a ultrasonic vibrator. In other words, the difference in the size of a capacity susceptance of a braking condenser, which various types of ultrasonic vibrators each possess, is compensated by the capacitive component. According to this structure, the composite capacitance value is kept constant even if the ultrasonic vibrators of the handpieces connected to the driving power-supply unit are of different types. In other words, even if the ultrasonic vibrators that are different from each other in the size of the capacity susceptance of the braking condenser are each connected to one inductor, namely, a common driving power-supply unit, the capacity susceptance of the braking condenser is always offset definitely (hereinafter, designated as xe2x80x9cmatchingxe2x80x9d). As a result, a resonance frequency peculiar to the ultrasonic vibrator coincides with a driving frequency of the driving power-supply unit.
However, if the ultrasonic vibrator and the capacitive component (condenser) are combined with each other, as described above, so as to bring about matching with respect to the driving power-supply unit, matching must be renewed by, for example, inspection or measurement when either the ultrasonic vibrator or the capacitive component (condenser) is repaired or replaced. This results in more complicated repairing and replacing operations requiring a great deal of labor.
It is an object of the present invention to, in a bolt-fastened Langevin type ultrasonic transducer, provide an ultrasonic vibrator that has a very versatile, simple structure which does not include a rotational structure, and is capable of infallibly preventing drops of water from entering the inside of the casing of the vibrator even if autoclave sterilization without a drying process is performed.
It is another object of the present invention to provide an ultrasonic vibrator capable of being easily replaced or repaired without performing an adjustment for offsetting the capacity susceptance of a braking condenser of the ultrasonic vibrator with respect to the inductor of a driving power-supply unit.
An ultrasonic vibrator of the present invention is characterized in that it comprises a transducer constructed by connecting a plurality of vibrating elements for converting a driving current into vibrations; an amplitude increasing portion for increasing an amplitude of a vibration of the transducer, the amplitude increasing portion having a horn at a front side thereof and a flange-shaped fixing portion at a base side thereof, the transducer being connected to the flange shaped fixing portion side; a cover covering the transducer; a supporting/fixing member for supporting and fixing the flange-shaped fixing portion to the cover in an airtight state by interposing a packing between the flange-shaped fixing portion and the cover; a lead wire for supplying the driving current to the plurality of vibrating elements; a partition member, disposed at the base side of the transducer, for defining a first chamber for passing the lead wire in an airtight state and containing the transducer in the cover in an airtight state; a member, fitted to a base side of the cover in an airtight state, for defining a second chamber for passing an electric power supply cord in an airtight state and drawing the electric power supply cord into the cover between the partition member and the member; and a plug for connecting the electric power supply cord to an electric power for generation of the driving current.
Other objects and advantages of the present invention will become sufficiently apparent from the detailed description given below.